The present invention relates to a process for the preparation of fluorinated vinylethers.
More specifically the present invention refers to the fluorohalogenether preparation which by dehalogenation produce the fluorinated vinylethers. The invention process leads to obtain fluorohalogenethers having improved selectivities.
As known, fluorinated vinylethers are a class of valuable monomers to obtain various polymers, from fluorinated elastomers to thermoprocessable semicrystalline fluorinated polymers.
Processes to obtain fluorohalogenethers based on the reaction of hypofluorites with olefins, are known in the prior art. For the hypofluorite preparation the most known processes use catalysts based on metal fluorides.
In U.S. Pat. No. 4,827,024 it is described the preparation in a continuous way of hypofluorite, by the fluorination reaction in equimolecular amounts with fluorine and halogenated carbonyl compounds having at least two carbon atoms, in the presence of catalysts formed of CsF as such or mixed with metals, such for example copper. Generally said metals are used, besides as catalyst (CsF) supports, also to make easier the thermal exchange, i.e. the dissipation of heat generated in the hypofluorite synthesis.
The metal support according to the above described prior art must satisfy two main functions: 1) to maintain the catalyst in a form accessible to reactants, 2) to make easier the thermal exchange maintaining under control in the required range the catalytic bed temperature. Last but not least a key feature of the support is the complete inertia towards reactants and reaction compounds.
In U.S. Pat. Nos. 4,816,599, 4,801,409 and 4,962,282 hypofluorites are preferably prepared with fluorine in excess to completely convert the acylfluoride into hypofluorite so that the acylfluoride concentration on the catalytic bed be very low, since it is known that some acylfluorides cause decomposition reactions in the presence of CsF. See for example Carl G. Ktrespan in Journal of Fluorine Chemistry, 16 (1980) 385-390.
Tests carried out by the Applicant on the prior art processes for the preparation of hypofluorites using the above catalysts have shown that by using both in a discontinuous and in a continuous way said catalytic systems, the catalytic activity rapidly decreases in the time. The Applicant has found in particular that the activity reduction is very marked, toll to the complete catalyst deactivation, when in the hypofluorite formation reaction the catalyst is used with an excess of fluorine over the stoichiometric value, the latter condition being indicated as preferred in the described prior art processes.
According to the prior art one must therefore operate in excess of fluorine in the hypofluorite synthesis to reduce as much as possible the above inconveniences. By operating under said conditions the catalyst of the prior art deactivates very rapidly, in two-three days. With so short durations it is in practice impossible to have available a continuous industrial plant.
Furthermore in discontinuous hypofluorite synthesis, when the catalytic bed is used in absence of support, its successive reuse in the hypofluorite obtainment reaction leads to very low yields and a very rapid deactivation is observed.
Processes to obtain fluorinated vinylethers are known in the prior art. U.S. Pat. No. 4,900,872 describes the perfluorovinylether precursor preparation, by continuous reaction between perfluoroalkyl hypofluorites diluted in an inert solvent and an olefin having formula CAIFxe2x95x90CAxe2x80x2IF, wherein A and Axe2x80x2, equal to or different from each other, are Cl and Br. In the patent it is indicated that said hypofluorites can be directly fed from the reactor wherein their synthesis in gaseous phase takes place, by reaction of fluorine with acylfluoride on catalyst. The obtained compounds are converted to perfluorovinylethers by dehalogenation with zinc. In said process the drawbacks are those reported above as to the hypofluorite preparation. In particular the drawback of said processes is due to the fact to have to synthesize and immediately use hypofluorites, which as known are unstable compounds, in particular when the number of carbon atoms of the hypofluorite perfluoroalkyl chain is higher than or equal to 2. Besides, in the hypofluorite synthesis it is known that one must use a catalyst, with the above drawbacks.
The need was therefore felt to have available a process for preparing fluorohalogenethers overcoming the drawbacks of the prior art.
The Applicant has surprisingly and unexpectedly found that by using the process described hereinafter it is possible to solve said technical problem, and therefore to have available a continuous or discontinuous industrial process having a very high selectivity.
An object of the present invention is a process to prepare (per)fluorohalogenethers having general formula (I):
(R)nC(F)mOCAFxe2x80x94CAxe2x80x2F2xe2x80x83xe2x80x83(I)
wherein:
A and Axe2x80x2, equal to or different the one from the other, are Cl or Br or one is selected from A and Axe2x80x2 and hydrogen and the other is halogen selected from Cl, Br; R can have the following meanings: F or a fluorinated, preferably perfluorinated, substituent, selected from the following groups: linear or branched C1-C20 alkyl more preferably C1-C10; C3-C7 cycloalkyl; aromatic, C6-C10 arylalkyl, alkylaryl; C5-C10 heterocyclic or alkylheterocyclic;
when R is fluorinated or perfluorinated alkyl, cycloalkyl, arylalkyl, alkylaryl it can optionally contain in the chain one or more oxygen atoms;
when R is fluorinated it can optionally contain one or more H atoms and/or one or more halogen atoms different from F;
n is an integer and is 1 or 2;
m is equal to 3-n;
by reaction of carbonyl compounds having formula (II):
(R)pC(F)q(O)xe2x80x83xe2x80x83(II)
wherein:
p is an integer and is 1 or 2;
q is an integer and is zero or 1,
with the proviso that when p=2, q=0; when p=1, q=1;
R is as above;
in liquid phase with fluorine and with olefinic compounds having formula (III):
CAFxe2x95x90CAxe2x80x2Fxe2x80x83xe2x80x83(III)
wherein A and Axe2x80x2 are as above, operating at temperatures from xe2x88x92120xc2x0 C. to xe2x88x9220xc2x0 C., preferably from xe2x88x92100xc2x0 C. to xe2x88x9240xc2x0 C., optionally in the presence of a solvent inert under the reaction conditions.
The fluorine used in the reaction can optionally be diluted with an inert gas such for example nitrogen or helium.
The formula (II) compounds which can be used are acylfluorides such for example COF2, CF3COF, C2F5COF, C3F7COF, C7F15COF, CF3CF(OCF3)CF2CF2COF, CF3O(CF2)2COF; ketones as hexafluoroacetone, perfluorodiisopropylketone, etc. Acylfluorides are preferred.
The formula (III) compounds are for example 1,2-dichloro-1,2-difluoroethylene (CFC1112), 1,2-dibromo-1,2-difluoroethylene, preferably CFC 1112.
The process according to the present invention is carried out in a single reactor and the reaction can be carried out in a semicontinuous or continuous way.
The semicontinuous process can be for example carried out by feeding gaseous fluorine in the reactor containing the formula (II) carbonyl compounds and the formula (III) olefinic compounds. The molar ratio (II)/(III) can range in a wide range, for example between 0.05 and 10. The fluorine feeding is continued until total olefin conversion. Said condition can be determined when the reaction exothermy is no longer noticed. In fact by carrying out the reaction of compounds (III) and (II) for example at xe2x88x92100xc2x0 C., as soon as the reaction compounds react with the elemental fluorine, there is exothermy and the temperature increases of about 5xc2x0-15xc2x0 C. Therefore the reaction ends when for example compound (III) has been completely consumed. At this point the reactor temperature comes back to the initial temperature.
In the continuous process the gaseous fluorine and compounds (II), (III) are fed into the reactor, until reaching the steady state. In practice the reactants are fed into the reactor with established flow-rates and the reaction mixture is continuously drawn. The steady state is reached when the concentration of the three reactants and of the reaction compounds in the reactor is equal to the concentration of the reactants and reaction compounds outflowing from the reactor.
The molar ratios among the reactants are not particularly binding for the present invention process, for example the (II)/(III) molar ratio can range from 0.05 to 10 and F2/(III) between 0.05 and 10.
As solvents in the present invention process, compounds which are liquid and inert in the above temperature range can be used. Compounds selected from (per)fluorocarbons, (per)fluoroethers, (per)fluoropolyethers, perfluoroamines, or respective mixtures, can be for example used. The skilled man in the art is able to select from the above classes the compounds to be used as solvents on the basis of their physical properties.
The Applicant has surprisingly and unexpectedly found that the reaction among a formula (II) compound, the formula (III) olefin and elemental fluorine, in the above temperature range, directly produces formula (I) fluorohalogenethers having an improved selectivity. This result is quite surprising and unexpected. Besides in the invention process no catalyst is used, as on the contrary indicated in the prior art for obtaining fluorohalogenethers from the hypofluorite precursor. Therefore the catalyst absence in the invention process notably simplifies the process, particularly on an industrial scale. Indeed the costs of the catalyst regeneration, of its substitution and generally of the management of the plant section comprising the catalytic reactor are very onerous.
The Applicant has found that by using the process of the prior art to obtain fluorohalogenethers by reaction between the olefin and the hypofluorite obtained from the corresponding acylfluoride, a high amount of hypofluorite decomposes. The hypofluorite decomposition reaction increases with its molecular weight; in practice it takes place if the hypofluorite is different from the methyl hypofluorite. See the comparative Examples. With the invention process there is an improved selectivity even when fluorohalogenethers deriving from the formula (II) compounds are prepared, independently from the number of R carbon atoms. In the invention Examples when the compound (II) is acetylfluoride or propionylfluoride the selectivity in the fluorohalogenether is substantially of the same order. Besides, compared with the prior art processes which use a catalyst to form the hypofluorites, the invention process has a higher productivity since the plant needs no stops for the catalyst regeneration or substitution. In the invention process the plant part concerning the catalyst preparation, the catalytic section running and the catalyst regeneration is therefore eliminated.
The Applicant has found that in the present invention process the decomposition products deriving from compound (II) are negligible. See the Examples.
Furthermore with the present invention process it is also possible to operate at compound (II) low conversions with high selectivity in the fluorohalogenether.
The formula (II) compounds, differently from hypofluorites which are unstable compounds, do not decompose in the reaction environment and can be recovered for example by distillation. When one operates with hypofluorites, this is not possible owing to the dangerousness of the use of said compounds both during the reaction and during the recovery. It is well known that when hypofluorites are used in the reaction they are let completely react without accumulation in the reaction environment.
The following Examples illustrate the invention with non limitative purposes.